716 BELL SYSTEM TECHNICAL JOURNAL 



struction. The driving motors depend upon the source of power of 

 each installation. Where the variation of the d-c. supply is greater 

 than ± 3 per cent, a speed regulator is provided. 



The generators of the double-voltage type have both a high and a 

 low- voltage winding. One supplies 10 amperes at 13 volts and 0.1 

 ampere at 200 volts to the receiver; the other 15 amperes at 13 volts 

 and 0.35 ampere at 1,050 volts to the transmitter. The units are 

 equipped with filters to prevent disturbance in the radio equipment. 



When voltage variations on shipboard are extreme, a 12-volt storage 

 battery may provide the filament source as well as operate both a 

 200-volt and a 1,050-volt dynamotor. The battery charger may be 

 of the automatic type or arranged for periodic charging. 



The control unit is designed for installation at any convenient 

 location. It provides facilities for remote starting and stopping the 

 radio apparatus. It consists essentially of a single master-control 

 switch, a telephone handset, call bell, a volume control for the receiver 

 in the handset, and an antennae meter for visual indication of the 

 transmitter operation, A small lamp on the unit indicates when 

 the receiver is in operation. To call or answer a call, one operates the 

 single master-control switch and removes the handset from its hook 

 switch. This controls the power to the radio transmitter, A push 

 button in the handset handle automatically switches from receive to 

 transmit position. 



As an adjunct to the two-way radio telephone system, a radio com- 

 pass has been developed which is essentially composed of a highly 

 sensitive radio receiver and of a loop and "sense-indicating" antenna, 

 and is extremely simple to operate. The accuracy of the arrangement 

 is in the order of one degree when 200 to 300 miles from the marine 

 radio beacon. Taking bearings on marine radio beacons is facilitated 

 by a scale on the receiver calibrated directly in kilocycles and a chart 

 on the receiver panel listing the radio beacons. After tuning, the loop 

 is rotated by a hand wheel until the needle of a center-reading meter 

 points to zero, A unique arrangement of the antenna permits a scale 

 on the shaft of the loop to indicate the azimuth between the ship's 

 heading and the direction of the received radio beacon when the meter 

 reads zero. As the loop is turned to the right or left, the needle on 

 the meter likewise swings to the right or left. There is no doubt as 

 to the "sense" of the bearing as the meter gives positive visual indica- 

 tion when the loop is rotated. By plotting the direction of the boat 

 from two or more radio beacons on the nautical chart, the intersection 

 of these plotted lines determines the ship's position. 



The direction-finding receiver employs a superheterodyne circuit, 



